Hitherto, wood free paper and the like represented in non-coated papers have been prevailingly used as transfer papers for xerography This is because images of higher quality cannot be obtained when general coated papers for graphic arts, including art paper and coat paper, are used in xerography. In other words, although the formation of an ideal toner image on a coated paper can be expected theoretically since the coated paper can uniformly contact with a photoreceptor because of its very high surface smoothness, the recording quality practically provided by the coated paper is almost equal to that provided by non-coated papers.
One of reasons therefor is that a coated paper causes the so-called blister phenomenon, or a phenomenon such that the base paper thereof swells at the surface part contacting with the coated layer, to lower the image quality. This blister phenomenon originates in that a general coated paper for graphic arts has insufficient gas permeability because the coated layer thereof comprises various adhesives in considerably large amounts in order to secure high surface gloss after printing and high surface strength upon printing. The insufficient gas permeability of the coated paper makes it difficult to let out the vaporized moisture in the base paper upon fixation with a heating roll during the copying operation, and so the vaporized moisture causes the swelling of the base paper at the surface part contacting with the coated layer.
As preventive measures taken against the blister phenomenon, for instance, Tokko Hei 5-82940 (the term "Tokko" as used herein means an "examined Japanese patent publication") proposes the method of controlling the air permeability of a coated paper, the so-called porosity, to no more than 4,000 seconds, and Tokkai Hei 1-245265 (the term "Tokkai" as used herein means an "unexamined published Japanese patent application") proposes the adjustment of the gas permeability of a raw paper and the water vapor permeability of a coated layer to their individually specified ranges;
Another reason why coated papers cannot provide images of high quality when they are used as transfer papers for xerography is that images formed on coated papers have uneven gloss. In general, after-copy gloss of a paper having low glossiness tends to increase with an increase in quantity of the toner transferred, because thorough fusion of color toner is necessary to satisfactory color development. In a case where the glossiness of a paper itself is heightened as described in Tokko Hei 5-82940, on the other hand, glossiness of halftone and highlight areas having a relatively small quantity of toner becomes all the lower for the uneven adhesion of toner although high glossiness can be obtained in the background area and the solid area having a very large quantity of toner. As a result of it, the gloss balance of an image as a whole becomes unsatisfactory.
Even if only the surface of a coated layer is improved, therefore, uniform and high image gloss akin to that obtained by a photographic printing paper cannot be ensured in a full-color image independently of the quantity of toner transferred.
As for the ink jet recording paper, on the other hand, Tokko Sho 63-22997 discloses the invention in which attention is directed to the void structure of a coated layer. In order to achieve the gloss akin to that of a photographic printing paper according to that inventions however, it is necessary to perform a surface treatment using a supercalender, a gloss calender or the likes Further, the achievement of high glossiness requires an excessive surface treatment, and thereby voids are destroyed to make it impossible to retain the original void structure.
Thus, there has yet been known any recording paper which can match a photographic printing paper in image quality when it is used as not only a transfer paper for xerography but also an ink jet recording paper to be applied to a recording system different from xerography.
In order to develop transfer papers for xerography which can provide full-color images of high quality, the Inventors have made intensive studies, and found that when not only the surface of a coated layer has a special void structure, e.g., by adjustment of the pigment/binder ratio in the coated layer to a specified range but also the surface roughness and glossiness of the coated layer are properly controlled, the paper provided with such a coated layer can be a highly satisfactory full-color transfer paper for xerography, and what is more, suitable for an ink jet recording paper, thereby achieving the present invention.